'Yet another good reason to tuck into that salad: Eating tomatoes could ward off depression' is the claim in the Daily Mail. It is based on a new study looking at whether there was an association between reported tomato consumption and depression…

The Daily Mail today reported that there is, “yet another good reason to tuck into that salad: eating tomatoes could ward off depression”.

Tomatoes are rich in lycopene, the chemical that gives them their distinctive colour. Lycopene is an antioxidant, a type of naturally occurring chemical believed to help protect against cell damage.

Previous research suggests foods high in antioxidants could have a preventative effect against physical diseases such as strokes. In this study, the researchers were interested in seeing if a similar preventative effect could also apply to depression.

The researchers assessed the mental health and dietary habits of 986 Japanese people aged over 70 years. They found that those who reported eating tomatoes two to six times a week were 46% less likely to report mild or severe symptoms of depression than those who said they ate tomatoes less than once a week. No such association was found for other vegetables.

This study has many limitations to consider, including a potential error in the way they measured dietary intake. Crucially, an inherent weakness of this type of research (a cross-sectional study) is that it can’t prove a direct cause and effect between reported tomato consumption and mental health.

It can also be subject to confounders. For example, it could be that in some cases, people who eat a lot of fresh fruit live a healthier lifestyle and take lots of exercise – and the exercise could be having the beneficial effects on mental health.

With those caveats in mind, this study is consistent with the advice that eating a healthy, varied and balanced diet is beneficial for both physical and mental health.

Low mood and depression

If you are feeling a little down, you may not really need treatment for depression. You can keep tabs on your mood by taking the mood self-assessment quiz which is part of the NHS Choices Moodzone.

Where did the story come from?

The study was carried out by researchers from Japanese and Chinese universities and was funded by grants from the Japanese Ministry of Education and Ministry of Health and the Japan Arteriosclerosis Prevention Fund. No conflicts of interest were declared.

The study was published in the peer-reviewed Journal of Affective Disorders.

The media coverage of the study was balanced and included a useful testimony from the researchers indicating that they could not be sure if lycopene in tomatoes directly affects the mind.

What kind of research was this?

This was a cross-sectional survey looking at the potential link between intake of vegetables and tomato products and depression.

The researchers state that defective antioxidant defences are related to symptoms of depression. That is, people who are more vulnerable to cell damage caused by ‘rogue’ molecules called free radicals, may also be more prone to experiencing depressive symptoms.

They were interested to investigate whether vegetables, which are known to be good sources of antioxidant chemicals, may have a protective effect. They were particularly interested in lycopene, a powerful antioxidant present in high levels in tomatoes.

Cross-sectional studies can only highlight associations – they cannot prove cause and effect (in this case, they can’t prove that eating tomatoes causes less depression or protects against it).

Depression and its causes are complex. The causes may include genetics, environment, and personal circumstances. Additional factors, outside of antioxidant intake, influence this relationship and this type of study is unable to account for them all.